1. Field of the Invention
The present invention relates to an improved device for enlarging the size of existing oil and gas well bore holes.
2. General Background
When drilling oil and gas wells, it is sometimes desirable to enlarge the size of the existing bore hole. "Hole openers", as the name applies, are used for this purpose. Hole openers are run at the end of a drill string, in place of the drill bit. Typically, hole openers have three primary parts, i.e., (1) the tool body, (2) blade members such as cutters, and (3) the bull nose. The tool body can be cylindrical having an internal bore and has blade members arranged around the exterior of the cylindrical body so that the outer diameter of the tool is larger than the inner diameter of the existing "hole" or well bore. A bull nose, usually affixed to the tool body by standard threaded connections, has an outer diameter somewhat smaller than the inner diameter of the bore hole. The bull nose serves as a guide to align and stabilize the tool body in the bore hole while the blade members are increasing the size of the hole. Blade members such as cutters are commonly affixed to the tool body by welding or by removable pins. A hole opener is usually removably attached to a drill string by means of standard A.P.I. pin and box connectors at the end of the tool opposite the bull nose.
Hole openers are related to other oil and gas well drilling tools such as mills, reamers, and to a lesser degree, stabilizers. Hole openers can differ from these tools in design, function, and position on a drill string. For example, reamers and stabilizers are usually run on a drill string in conjunction with a drill bit, whereas hole openers and mills are run in place of a drill bit. While hole openers are used to enlarge an existing bore hole, mills are used to grind up debris in the bore hole, to remove stuck portions of drill stem or sections of casing for sidetracking and to ream out tight spots in the casing. Reamers are used to smooth out the wall of the well, to help stabilize the bit, to straighten the bore hole if it "doglegs", to drill directionally, and to enlarge the bore hole to a specified size. Stabilizers are used to either change the deviation angle in a well or to maintain the correct hole angle.
Features common to hole openers, mills, reamers and stabilizers are blade members, annular flow zones and circulation jets. The annular flow zones generally span the distance between the blade members so that fluid can circulate in the bore hole during drilling operation. Circulation jets in the tools allow fluids to flow out of the internal bore of the tool body and into the well bore, to remove cuttings from the well bore to the surface, and to maintain the hydrostatic pressure in the well.
There are two problems typically associated with the operation of hole openers. These two problems are often found in the operation of reamers, mills and stabilizers as well. These problems are the loss of blades in the hole and the "balling up" of blades with shale cuttings. Blades are commonly affixed to the tool body by means of pins or welds. The extreme pressures encountered in drilling operations weaken the connections and cause the blade to break away from the tool body. It is sometimes necessary to remove the drill string from the hole and use a fishing tool to retrieve the blade. Fishing for these broken blades can be a time-consuming and costly operation.
In soft, unconsolidated formations such as the gumbo shale found in the Gulf of Mexico, tools having limited area annular flow zones between the blades that become "balled-up" with cuttings. Once the blades are "balled-up", the tool loses its effectiveness. Additionally, as a balled-up tool is removed from the well bore, it may prevent drilling fluids from circulating along the length of the bore hole. The hydrostatic pressure in the hole may then become unequalized and a kick or blowout condition may result.
Hole openers, mills, reamers and stabilizers of various designs are commercially available. Representative of the hole openers available are those of Security, a division of Dresser Industries. These hole openers have integral bodies, interchangeable cutters and circulation jets. Security's hole openers do not have three longitudinally, radially spaced apart blades that are parallel to the central axis of the tool body. Nor do the Security hole openers have three annular flow zones that span the distance between the blade members.
Eastman Oil Well Survey Company has an "Eastco" two cutter hole opener. The entire body is cast from a single piece of steel, gut it has roller cutters which are secured to the tool body by pins or bolts. Roller cutters are susceptible to balling up in soft formations. The bull nose is solid, i.e., it does not have an internal bore through which fluids can be circulated.
American Iron and Machine Works, Inc. has a roller reamer that may be converted into a hole opener by replacing the reamer blades with cutter blades. The blades are affixed by pins and are susceptible to being lost in the hole. The pilot section of this tool appears to be in a "fish-tail" configuration. A pilot so designed will cause an existing well bore to become sidetracked if the fishtail digs into the wall of the well bore. Sidetracking occurs frequently in soft unconsolidated formations and in directional wells.
Parko, Inc. is the assignee of U.S. patent application Ser. No. 702,647 filed Feb. 14, 1985 for a reamer having three longitudinal, radially spaced apart blade members that are parallel to the central axis of the tool body. The blades are an integral portion of the tool body. The Parko reamer does not have a pilot and a bull nose. The blade members of the Parko reamer do not converge with the annular flow zone to form a channel means to receive and sweep away cuttings from the blade members as the size of the bore hole is enlarged.
In the prior art of hole openers, mills, reamers and stabilizers, there are patents which address the configuration and design of these types of tools. These patents include those listed below:
U.S. Pat. No 3,645,587 issued to Bill G. Parker entitled "Drill String Member and Method of Manufacture" shows a bottom hole stabilizer having three longitudinal, radially spaced apart blade members that are parallel to the central axis of the tool body with three annular flow zones which span the distance between the blade members. The tool shown by this invention is used to center a drill string in the bore hole in order to avoid deviation. This tool has upper and lower attachment means so that it can be placed above the bit in a drill string.
U.S. Pat. No. 3,147,536 issued to D. E. Lamphere entitled "Apparatus for Milling Tubular Strings in Well Bores" shows a mill used to grind debris in a hole and to remove tubular conduits, such as liners and casings. The apparatus has cutter blades placed around the circumference of the tool body and annular flow zones between the cutter blades. The lower portion of the cutter blades are designed to break away in the hole after a section of tubular conduit has been removed. The bull nose or pilot of the apparatus is short and wedge-shaped which make the tool difficult to use in soft formations and deviated wells since it can easily sidetrack.
U.S. Pat. No. 4,350,204 issued to Gary B. Horton, entitled "Reamer" is a device for removing paraffin, scale, ice and other accumulations from the inside services of oil well pump tubing and casing. The tool is run on a wireline and swivel joint and not on a drill string. While the tool does have an internal bore, the bore is not designed for the circulation of drilling fluids through it. Circulation of fluids is needed in order to rotary drill or to enlarge a bore hole. The apparatus has removable blades that are bolted to the tool body.
U.S. Pat. No. 3,114,416 issued to A. W. Kammerer entitled "Liner Hanger and Liner Milling Tool" shows a tool designed to run in a cased, rather than open hole. The tool body has multiple blade members spaced around its circumference with limited annular flow zones between the blade members. These design features make a tool susceptible to becoming balled-up in soft, unconsolidated formations. The tool has a short wedge-shaped pilot or bull nose designed for milling in a cased hole but which will cause sidetracking in an open hole since it will dig into the walls of soft formations.
U.S. Pat. No. 4,385,669 issued to Paul Knutsen entitled "Integral Blade Cylindrical Guage Stabilizer Reamer" is a tool designed to grind the circumference of the bore hole shortly after it has been cut by the drill bit. The tool helps to maintain the diameter of the bore hole as the drill bit passes through formations. The apparatus has blade members that spiral around the circumference of the tool body. The annular flow zones are limited so the tool is more useful in hard rock formations than in soft formations where balling up is a problem.
Russian Pat. No. 594,289 dated Feb., 1978 is very similar to the Knutsen patent. This apparatus is a bore hole guaging tool similar to a reamer. It has vanes which spiral around the tool body. Channels between the vanes are used to move cuttings up and out of the hole to keep the bottom of the hole clean. It does not have a pilot or bull nose since it is used in conjunction with a drill bit.
French Patent No. 1,407,504 issued Sept. 11, 1964 to The Birmingham Small Arms Company Limited appears to be a casing scraper, key seat wiper or packer. The apparatus does not have longitudinally extending blade members, a pilot, bull nose or circulation jets. Nor does it appear to have an internal bore for the passage of fluids.
U.S. Pat. No. 3,610,350 issued to Ed. O. Seabourn, on Oct. 5, 1971 is a rotary drill bit having chamber, annular and sidewall cutting elements for cutting an undersea wellhead and receiving the wellhead within the bit. The tool is not designed to be run on a drill string in a bore hole to enlarge the size of a bore hole. While it does have an internal bore and three longitudinal, radially spaced apart blade members that are parallel to the central axis of the tool body bore, it does not have a pilot or bull nose to guide the tool through an existing well bore.